The present invention relates to a plastic zipper having improved durability which permits easy opening, hermetical resealing after opening, and repeated opening/closing operations of more than 100 times without losing resistance to opening to be widely used in simplified containers for packaging foods, pharmaceuticals and the like, and a container with said plastic zipper.
Flexible packaging materials with plastic zippers have conventionally been used as containers for packaging various types of products by virtue of advantages thereof such as light weight, inexpensiveness, easy recyclability, high volume reduction ratio and the like and, for the reasons of advancement in hermetical sealing performance and low cost, has recently come to be used in applications for packaging products such as nutritional supplements, decolorants and the like which are frequently used but in a small quantity at a time.
However, although a conventional plastic zipper comprising a male hook and a pair of female hooks is excellent in hermetical sealing performance and resealing ability, it has problems that, when opening/closing operations exceed 30 times, a sealing function thereof is deteriorated to an unusable degree, or when it is subjected to a high temperature or a low temperature, an opening/closing function thereof is deteriorated; hence it has been desired to solve these problems.
Cross-sectional configurations as shown in FIGS. 2 to 5 have been adopted for conventional plastic zippers. In any of the configurations, a hook form on a content side is, as shown in FIGS. 2 to 5, a combination of talons of male and female hooks in an engaged state while an opening side of one or both of the male and female talons is in arc form in an engagement portion therebetween as shown in FIG. 4A or has an obtuse angle compared with talons on the content side (FIG. 4B) thereby effecting a weaker engagement strength than that of the hooks on the content side.
An engagement function of the conventional plastic zipper is explained with reference to FIG. 2.
That is, a male hook 13 is pinched by and interlocked with female hooks 14, 15 each having an increased rigidity so that, even if flanges 11, 12 which are connected to respective base portions thereof are pushed for opening in respective directions of L and Lxe2x80x2 by an opening force from the content side, the male hook 13 and the female hook 14 which are engaged and interlocked with each other in combination as shown in FIG. 4B will not be freed.
In order to maintain a state pinched (engaged) by the female hooks 14, 15 on this occasion, it is necessary to increase rigidity of the female hook as a whole whereupon the higher the above-described rigidity, the higher resistance to opening from the content side. When the above-described rigidity is weak, the female hooks 14, 15 are bent thereby freeing the thus formed interlock.
A zipper shown in FIG. 3 has the same function of opening as that in FIG. 2; however, since a thickness of a flange portion thereof is larger than that in FIG. 2, the rigidity thereof is conceivably higher than the latter one.
A gap (Y-Z) between a space Y defined by a tip B14 of the talon of the female hook 14 on the content side and a tip B15 of the talon of the female hook 15 on the opening side as shown in FIG. 2 and a thickness Z of a base portion of the male hook 13 is an important factor; there exists a tendency that the narrower the gap, the stronger the resistance to opening, while the wider the gap, the weaker the resistance to opening; therefore, it is necessary to perform an accurate control on the above-described gap whereupon difficulty in such control deteriorates a production yield causing an increase in production cost.
When an opening operation is executed from the opening side, since a female talon of the female hook 15 on the opening side has the portion in arc form as illustrated in FIG. 4A, the tip B15 of the talon of the female hook 15 move slidably along the portion in arc form of the male hook 13 as the flanges 11, 12 are opened in respective directions of O and Oxe2x80x2 whereupon the female hook 15 slightly bends to the opening side thereby enabling the engagement between the female hook 15 and the male hook 13 to be freed without necessitating a large quantity of opening force.
When the opening side of the plastic zipper is opened and, accordingly, the interlock is freed, the engagement on the content side is easily freed.
In the conventional plastic zipper, resistance to opening necessary for opening from the content side in a state in which talons are engaged with each other can be held at from about 5 kg/5 cm to about 7 kg/5 cm which are strong enough and resistance to opening necessary for opening from the opening side can be held at from about 0.6 kg/5 cm to about 1.5 kg/5 cm which are easy enough to open within 10 times of opening/closing operations; however, when opening/closing operations are repeated more than 10 times, the resistance to opening on both content and opening sides are decreased whereupon an opening/closing function can not be maintained any longer.
In the conventional plastic zipper, it has been required that the resistance to opening on the content side is strong whereas the resistance to opening on the opening side is weak. However, with reference to the zipper in the same form, when the resistance to opening on the content side becomes strong over a certain limit, that on the opening side inevitably becomes strong; to contrast, when resistance to opening on the content side becomes weak, that on the opening side inevitably becomes weak.
For this reason, an effort has hetherto been made such that, in order to increase the resistance to opening on the content side, rigidity of the female hook as a whole is increased or a size of a hook on the content side is enlarged, whereas, in order to reduce the resistance to opening on the opening side, an arc shape of the hook on the opening side is adjusted or in order to make a balance in strength between the content side and the opening side, the gap (Y-Z) between the female hook and the male hook is adjusted.
However, in the conventional plastic zipper, it is inevitable that the female hook slightly undergo a plastic deformation outward and the gap (Y-Z) between the female hooks and the male hook is gradually broadened every time an opening/closing operation is performed in a repeating way.
As a result, as a number of frequencies of opening/closing operations is increased, the resistance to opening on the opening side becomes weaker and weaker whereupon the resistance to opening is reduced by about 20 times of opening/closing operations in a type shown in FIG. 2 and by about 30 times of opening/closing operations in a type having a higher rigidity shown in FIG. 3 so that it presents a defect that the resistance to opening can not be held high enough.
Further, in the plastic zipper, the plastic deformation of the plastic material largely depends on temperatures so that there exist a problem that there are many cases in which the resistance to opening can not be held at an elevated temperature, the female hook become brittle at a low temperature and can not be bent thereby causing an engagement problem in hooks and so forth.
In the plastic zipper shown in FIG. 5, in order to increase the sense of stiffness to a finger at the time of opening/closing operations, rigidity between the female hooks 14 and 15 is increased and, further, a guide rib is provided or the male hook is separated into halves; however, the opening function thereof remains basically identical to those of the plastic zippers shown in FIGS. 2 and 3 and, even though such measures described above are taken, a problem of durability of the plastic zipper is not solved.
It is an object of the present invention is to develop a plastic zipper capable of adjusting resistance to opening on each of content and opening sides and permitting resistance to opening on an opening side to consistently hold a low value of from about 0.9 kg/5 cm to about 1.2 kg/5 cm while permitting resistance to opening on a content side of the zipper to hold substantial strength of from about 7 kg/5 cm to about 8 kg/5 cm and, further, capable of maintaining resistance to opening on each of the content and opening sides close to an initial one even after opening/closing operations have been executed 100 times or more.
The present invention has solved the above problems by developing:
(1) A plastic zipper comprising a male hook and a pair of female hooks that are engaged with each other to form a combination thereof, wherein the pair of female hooks is placed on a portion of flange which portion is made to flex by an opening force when applied to the plastic zipper from an opening side thereof, said portion being defined by base portions of two female hooks on the opening and content sides;
(2) A plastic zipper comprising a male hook and a pair of female hooks that are engaged with each other to form a combination thereof, wherein a base portion of the talon of the female hook on the content side is disposed to the content side over a base portion on the content side of said female hook, while the a base portion on the opening side of the female hook on the opening side is disposed to the opening side over a base portion of the talon of the female hook on the opening side;
(3) A plastic zipper comprising a male hook and a pair of female hooks that are engaged with each other to form a combination thereof, wherein a base portion on a content side of the male hook is disposed to the content side over a tip of the talon on the content side of said male hook, while a base portion on the opening side of said male hook is disposed to the content side over a tip of the talon on the opening side of said male hook;
(4) A plastic zipper which comprises in combination, the pair of female hooks set forth in at least any one of the above-described (1) and (2) and the male hook set forth in (3); and
(5) A container for packaging wherein use is made of the plastic zipper set forth in any one of the above-described (1) to (4) as an opening/closing device for the container.